The lockout at the Thane plant, which employs 212 people, would have no impact on the group's supply of medicines, a Pfizer Ltd spokesman said in a statement emailed to Reuters.
Work would not resume at the factory until it was assured of the safety of all staff, the statement said, without saying why the unrest had occurred. Nor did it give details on the threats or attempts at disruption it had cited.
"There have been multiple incidents of indiscipline, threats to our management personnel as well as attempts to disrupt production lines by certain workmen," the statement said.
Apart from the Thane plant, Pfizer Ltd also owns one other drug factory in India in the western state of Goa.